University of Bristol research discovers 'hidden power' of the human eye

Human eyeballs can see a feature of light believed to be the exclusive ability of certain creatures like bees, octopuses and cuttlefish.

This is a property of light called polarisation where the oscillations of light waves are in one particular direction.

Research at the University of Bristol demonstrated that the human eye can pick out polarised light, even if for a few seconds only.

Look for the "Haidinger's brushes" or yellow shaped bows on the white LCD screen of a computer or phone by tilting your head from side to side.

A bluish bow can also be seen at right angles to the yellow one, says Shelby Temple from the University of Bristol, who conducted the research.

The bow-ties, slightly larger than a thumb, can also be seen with some practice in blue skies at 90 degrees from the sun – meaning at sunrise and sunset. The long axis of the yellow bow-tie will point approximately towards the sun, writes research associate Juliette McGregor in The Conversation.

As the bow is not a real external object but an effect, it will disappear after the brain processes the information.

Among 24 people who took part in Temple's study, the average polarisation sensitivity threshold was 56%.

The researchers believe polarised light detection could help screen people at risk of age-related macular degeneration - a leading cause of blindness, by looking at the organization of pigments in the eye.

Polarisation of light
Ordinary light is made of electromagnetic waves oscillating in all directions. Polarised light is the filtered component which oscillates in one direction, like a skipping rope shaken side to side, or up to down.

Light falling on your computer screen and in reflections from water or glass is largely polarised.

Polarised light is the technology behind modern 3D cinema and LCD computer screens, dark glasses, smartphones and tablets.

Light is polarised when it is reflected from a transparent material, such as glass or even by transmission through certain materials. Refraction and scattering (as happens in the sky) also polarises light.

Invertebrate animals use polarised light to navigate, find water, detect prey or predators, or for communication. Temple thinks ancient humans probably did the same too when the sun was not visible during the daytime (at northern latitudes).